1. Field of the Invention
The present invention relates to diamonds, and more particularly, to a tough diamond produced using Microwave Plasma Chemical Vapor Deposition (MPCVD) within a deposition chamber.
2. Description of Related Art
Large-scale production of synthetic diamond has long been an objective of both research and industry. Diamond, in addition to its gem properties, is the hardest known material, has the highest known thermal conductivity, and is transparent to a wide variety of electromagnetic radiation. It is valuable because of its wide range of applications in a number of industries, in addition to its value as a gemstone. However, a diamond can have low fracture toughness that will makes it unsuitable for many applications, such as a high impact machine tools.
For at least the last twenty years, a process of producing small quantities of diamond by chemical vapor deposition (CVD) has been available. As reported by B. V. Spitsyn et al. in “Vapor Growth of Diamond on Diamond and Other Surfaces,” Journal of Crystal Growth, vol. 52, pp. 219-226, the process involves CVD of diamond on a substrate by using a combination of methane, or another simple hydrocarbon gas, and hydrogen gas at reduced pressures and temperatures of 800-1200° C. The inclusion of hydrogen gas prevents the formation of graphite as the diamond nucleates and grows. Growth rates of up to 1 μm/hour have been reported with this technique.
Subsequent work, for example, that of Kamo et al. as reported in “Diamond Synthesis from Gas Phase in Microwave Plasma,” Journal of Crystal Growth, vol. 62, pp. 642-644, demonstrated the use of Microwave Plasma Chemical Vapor Deposition (MPCVD) to produce diamond at pressures of 1-8 Kpa in temperatures of 800-1000° C. with microwave power of 300-700 W at a frequency of 2.45 GHz. A concentration of 1-3% methane gas was used in the process of Kamo et al. Maximum growth rates of 3 μm/hour have been reported using this MPCVD process.
In the above-described processes, and in a number of more recently reported processes, the fracture toughness of the diamonds is better in some instances than natural diamond. In particular, higher-growth rate processes that only produce or grow polycrystalline forms of diamond are known to produce diamond having a fracture toughness higher than natural diamond. Other than some high pressure high pressure (HPHT) synthetic diamonds, which have been annealed, most diamonds have a fracture toughness of less than 11 MPa m1/2.